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The mediastinum (from Medieval Latin mediastinus, "midway"[1]) is the central compartment of the thoracic cavity surrounded by loose connective tissue, as an undelineated region that contains a group of structures within the thorax. The mediastinum contains the heart and its vessels, the esophagus, trachea, phrenic and cardiac nerves, the thoracic duct, thymus and lymph nodes of the central chest.

3D rendering of a high resolution computed tomography of the thorax, with mediastinum marked in blue.
Mediastinum. The division between superior and inferior is at the sternal angle.
Latin mediastinus
TA A07.1.02.101
FMA 9826
Anatomical terminology



The mediastinum can be seen from a frontal view in this illustration, with the superior mediastinum labeled a, and the pericardial cavity, which is part of the inferior mediastinum labeled d.
The mediastinum can not be seen in a lateral projection, as it is hidden behind the thoracic cavity 2 in this schematic, of which only the pleural cavity is visible.

The mediastinum lies within the thorax and is enclosed on the right and left by pleurae. It is surrounded by the chest wall in front, the lungs to the sides and the spine at the back. It extends from the sternum in front to the vertebral column behind, and contains all the organs of the thorax except the lungs. It is continuous with the loose connective tissue of the neck.

The mediastinum can be divided into an upper (or superior) and lower (or inferior) part:

  • The superior mediastinum starts at the superior thoracic aperture and ends at the thoracic plane.
  • The thoracic plane separates the superior and inferior mediastinum. It is a plane at the level of the sternal angle, and the intervertebral disc of T4–T5.[2][3][4]
  • The inferior mediastinum from this level to the diaphragm. This lower part is subdivided into three regions, all relative to the pericardium – the anterior mediastinum being in front of the pericardium, the middle mediastinum contains the pericardium and its contents, and the posterior mediastinum being behind the pericardium.

Anatomists, surgeons, and clinical radiologists compartmentalize the mediastinum differently. For instance, in the radiological scheme of Felson, there are only three compartments (anterior, middle, and posterior), and the heart is part of the anterior mediastinum.[5][page needed]

Superior mediastinumEdit

The superior mediastinum is bounded:

Mediastinum anatomy.
Some mediastinal structures on a chest radiograph.

Thoracic planeEdit

A number of structures occur at the level of the thoracic plane, which divides the superior and inferior mediastinum:

Structures at the level of the thoracic plane edit
  1. The start and end of the aortic arch
  2. The division between the superior and inferior mediastinum
  3. The upper margin of the superior vena cava [9]
  4. The crossing of the thoracic duct
  5. The bifurcation of the trachea [10]
  6. The bifurcation of the pulmonary trunk
  7. The level of the sternal angle
  8. The level of Rib 2 where it attaches to the sternum via the 2nd costal cartilage
  9. The body of vertebrae T4 (the disc between the vertebrae T4 and T5)
  10. The drainage of the azygos vein into the superior vena cava
  11. thymus gland(in some cases)

compiled by

Inferior mediastinumEdit

Anterior mediastinum

Is bounded:

  • superior and inferior sternopericardial ligaments
Middle mediastinum

Bounded: pericardial sac – It contains the vital organs and is classified into the serous and fibrous pericardium.

Posterior mediastinum

Is bounded:

  • Anteriorly by (from above downwards);bifurcation of trachea; pulmonary vessels; fibrous pericardium and posterior sloping surface of diaphragm
  • Inferiorly by the thoracic surface of the diaphragm (below);
  • Superiorly by the transverse thoracic plane;
  • Posteriorly by the bodies of the vertebral column from the lower border of the fifth to the twelfth thoracic vertebra (behind);
  • Laterally by the mediastinal pleura (on either side).

Clinical significanceEdit

Mediastinal adenopathy

The mediastinum is frequently the site of involvement of various tumors:

  • Anterior mediastinum: substernal thyroid goiters, lymphoma, thymoma, and teratoma.
  • Middle mediastinum: lymphadenopathy, metastatic disease such as from small cell carcinoma from the lung.
  • Posterior mediastinum: Neurogenic tumors, either from the nerve sheath (mostly benign) or elsewhere (mostly malignant).

Mediastinitis is inflammation of the tissues in the mediastinum, usually bacterial and due to rupture of organs in the mediastinum. As the infection can progress very quickly, this is a serious condition.

Pneumomediastinum is the presence of air in the mediastinum, which in some cases can lead to pneumothorax, pneumoperitoneum, and pneumopericardium if left untreated. However, that does not always occur and sometimes those conditions are actually the cause, not the result, of pneumomediastinum. These conditions frequently accompany Boerhaave's syndrome, or spontaneous esophageal rupture.

Widened mediastinumEdit

Widened mediastinum
Synonyms Mediastinal widening
Widened mediastinum in a patient with achalasia
Classification and external resources
ICD-9-CM 519.3
DiseasesDB 29459

Widened mediastinum/mediastinal widening is where the mediastinum has a width greater than 6 cm on an upright PA chest X-ray or 8 cm on supine AP chest film.[11]

A widened mediastinum can be indicative of several pathologies:[12][13]

See alsoEdit


This article incorporates text in the public domain from the 20th edition of Gray's Anatomy (1918)

  1. ^ Mediastinum dictionary definition
  2. ^ Thoracic Wall, Pleura, and Pericardium – Dissector Answers
  3. ^ Untitled Document
  4. ^ UAMS Department of Anatomy – Topographical Anatomy – Thorax
  5. ^ Goodman, Lawrence. Felson's Principles of Chest Roentgenology. 
  6. ^ Thoracic Wall, Pleura, and Pericardium – Dissector Answers
  7. ^ Untitled Document
  8. ^ UAMS Department of Anatomy – Topographical Anatomy – Thorax
  9. ^ Arai et al. Radiographic landmarks of the upper margin of the superior vena cava (SVC) in children Canadian Journal of Anesthesia 49 (Supplement 1): 32
  10. ^ Viscera of the Thorax UAMS Department of Anatomy
  11. ^ D'Souza, Donna. "Thoracic aortic injury | Radiology Reference Article |". 
  12. ^ Geusens; Pans, S.; Prinsloo, J.; Fourneau, I. (2005). "The widened mediastinum in trauma patients". European Journal of Emergency Medicine. 12 (4): 179–184. doi:10.1097/00063110-200508000-00006. PMID 16034263. 
  13. ^ Richardson; Wilson, M. E.; Miller, F. B. (1990). "The widened mediastinum. Diagnostic and therapeutic priorities". Annals of Surgery. 211 (6): 731–736; discussion 736–7. doi:10.1097/00000658-199006000-00012. PMC 1358125 . PMID 2357135. 
  14. ^ Chandra S, Laor YG (April 1975). "Lung scan and wide mediastinum". J. Nucl. Med. 16 (4): 324–5. PMID 1113190. 
  15. ^ von Kodolitsch Y, Nienaber C, Dieckmann C, Schwartz A, Hofmann T, Brekenfeld C, Nicolas V, Berger J, Meinertz T (2004). "Chest radiography for the diagnosis of acute aortic syndrome". Am J Med. 116 (2): 73–7. doi:10.1016/j.amjmed.2003.08.030. PMID 14715319. 
  16. ^ Jernigan JA, Stephens DS, Ashford DA, et al. (2001). "Bioterrorism-related inhalational anthrax: the first 10 cases reported in the United States". Emerging Infect. Dis. 7 (6): 933–44. doi:10.3201/eid0706.010604. PMC 2631903 . PMID 11747719. 
  17. ^ Gideon P. Naudé; Fred S. Bongard; Demetrios Demetriades (2003). Trauma secrets. Elsevier Health Sciences. pp. 95–. ISBN 978-1-56053-506-5. Retrieved 19 April 2010. 

External linksEdit

  • Anatomy figure: 21:01-03 at Human Anatomy Online, SUNY Downstate Medical Center – "Divisions of the mediastinum."
  • Anatomy figure: 21:02-03 at Human Anatomy Online, SUNY Downstate Medical Center – "The anatomical divisions of the inferior mediastinum."
  • thoraxlesson3 at The Anatomy Lesson by Wesley Norman (Georgetown University) – "Subdivisions of the Thoracic Cavity"